Having some POWER to the GLOW PLUGS problems the last few weeks. Not working again. I'm thinking the pre-glow time relay is bad. Would there be power to the relay all the time when the key is switched on ? I know the relay shuts off after 30 seconds, but is there still power to it after that happens?

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1984 MB 300SD Turbo

IIIRC the glow plug relay always has power. Did you check the fuse? It's on the top of the relay under the cover.

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1991 350SDL. 230,000 miles (new motor @ 150,000). Blown head gasket

Tesla Model 3. 205,000 miles. Been to 48 states!
Past: A fleet of VW TDIs.... including a V10,a Dieselgate Passat, and 2 ECOdiesels.
2014 Cadillac ELR
2013 Fiat 500E.

Yes. Same when the key is switched off.

Yes, there is power in the box. I'm off to the pick & pull.

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1984 MB 300SD Turbo

There's actually two power inputs: one from the battery that is alway on regardless of key position, and a second from the switch that is on only in the run position. If you have a bad connection between the battery and the GP relay, or if your GP relay internal fuse is dodgy you might confuse this with a relay problem. Better to check the connections and operating voltages (voltages at the GPs when relay is energized, switched voltage to relay, ground connections, engine ground, etc.) first before replacing parts. Also, take the fuse out of the relay and make sure it is in one piece. Sometimes they develop a hairline crack that interferes with proper operation.

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mjk

'84 300SD 119KMi (Liesl der Diesel)
'84 300D 326KMi when the oil left (former parts car)
'82 300SD 253KMi (new parts car)